Widely known in the art are power hammers with the head-on movement of ram and bolster each whereof incorporates a power frame accommodated in guides of a stationary main frame with provision for vertical displacements and carrying a bolster (bottom die) giving support to a blank and also an actuating cylinder provided with a space below the piston filled with a gas under a pressure for returning the piston into, and retaining it in, the initial position as well as with a space above the piston serving as a gas chamber whereas attached to the piston rod is a ram with a top die. Each of such hammer is provided with a means of accelerating the power frame by a force which is equal to, or exceeds by a specified amount, its weight.
As far as the known hammers are concerned said means of accelerating consists of an air cylinder fitted to the main frame so that the piston rod abuts against the lower surface of the power frame. In the known hammers, the movement of the ram and bolster toward each other and, consequently, the movement of those structural members to which the ram and bolster are attached is induced by the action of a compressed gas admitted simultaneously into the gas chamber and the space under the piston of the air cylinder from an air line. To prevent shock loads from coming on the main frame of the hammer, the movement of the structural members towards each other must take place due to the effect of such momentum of these members (i.e., the product of their mass and velocity) which causes the power frame to come to a halt on striking the blank and then to settle gradually into its initial position as soon as the gas is bled from the air cylinder.
This requirement can be fulfilled if at the instant of the stroke the ratio of the momentum of the power frame integrally with the bottom die to that of the piston integrally with the piston rod, ram and top die is either unity while subject to forging is a blank displaying plastic deformation (the stroke recovery factor is zero in this case) or is greater than unity by a certain amount depending on the stroke recovery factor when forged is a blank displaying both plastic and elastic deformation (the stroke recovery factor is other than zero in this case).
To achieve in the known hammers an equilibrium between the momentums of the structural components striking against each other, the force exerted by the air cylinder is to be equal to the weight of the power frame, but to give the power frame a momentum exceeding the momentum of the piston integrally with the piston rod, ram and top die, the force developed by the air cylinder must exceed the weight of the power frame by a certain amount.
Since the force exerted by the air cylinder is the product of the cross-sectional area of the piston and the air pressure while for each particular hammer the weight of the power frame is a constant, it stands to reason that the specified ratio of the momentums of the members striking against each other is obtainable in the known hammers with a definite cross-sectional area of the piston by maintaining the gas pressure in the air line at a quite definite level. Should it occur that the gas pressure rises above this level, the consequence is that the power frame continues its upstroke after a blow has been delivered against the blank and thus gains potential energy which, on being transformed into kinetic energy, is transmitted to the main frame of the hammer in the form of a shock load. On the other hand, a gas pressure below the specified level causes a downward displacement of the power frame after the blow against the blank with the result that the main frame of the hammer will also be exposed to a shock load.
Taking into account that the shock loads the main frame and foundation of the hammer are subject to produce seismic effects detrimental to the surroundings, it is desirable to keep these loads as low as possible. This implies that in the known hammers the pressure of gas in the gas chamber and in the space below the piston of the air cylinder should not appreciably differ from the specified value. Inasmuch the blow energy the hammer possesses is controlled by the pressure of gas in the gas chamber, said energy can be changed in the known hammers only over a relatively narrow range which is a factor impairing processing capability of the hammer.
Another point is that in the known hammers the movement of the ram and bolster towards each other during each cycle is preceded by the bleeding of compressed gas from the space below the piston of the actuating cylinder and, moreover, the power frame returns into its original lowermost position while compressed gas in being bled from the space below the piston of the air cylinder. The consequence is high consumption of compressed gas and poor economy of the hammer.